Sound source probing system

ABSTRACT

In order to locate and display the source of a sound such as a noise at a factory or the like accurately even when it is outside, a pair of microphones (M 1 , M 3 ) and another pair of microphones (M 2 , M 4 ) are disposed on the X axis and Y axis with a distance L therebetween, respectively, the direction of the sound source is estimated from a difference between sound arrival times to the microphones (M 1 , M 3 ) and a difference between sound arrival times to the microphones (M 2 , M 4 ), an image around the estimated location of the sound source is picked up by a camera, and the above estimated location of the sound source is displayed on the above image displayed on the display of a personal computer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sound source locating systemfor locating the source of a noise and displaying the location of thesource to cope with noises at a factory or the like.

[0003] 2. Description of the Prior Art

[0004] At a factory or the like, many kinds of low-frequency noiseshaving a frequency of 50 Hz to 60 Hz or a frequency double thatfrequency are generated from a power supply box and a transformer suchas a relay. To cope with such noises, an operator measures a soundpressure distribution around a noise generating device with a noisemeter to locate the source of the noise and take countermeasures againstit. However, it is time-consuming and not efficient to locate thesource. Then, a method of estimating the source of a sound such as anoise using an acoustic technique is now under study.

[0005] Conventionally proposed sound source locating methods include (1)one making use of the correlation between sound pressure waveforms and(2) one making use of acoustic holography. In the method (1), theproperty of a correlation function is utilized to estimate the locationof a sound source from the correlation between sound waveforms collectedat a plurality of locations whereas in the method (2), a basic wave isscanned in a space to be investigated, an interference sound generatedby interference between the above basic wave and a noise is recorded foreach scanning direction, and a sound pressure distribution in the spacein which the basic wave has been scanned is reproduced from the obtainedrecord to estimate the source of the noise.

[0006] Although measurement and analysis take long in the above methodmaking use of the correlation between sound pressure waveforms and theabove method making use of acoustic holography, the methods areeffective in a limited space but have a problem that a system becomeslarge in size to improve accuracy when a sound source is locatedoutside.

[0007] It is conceivable that a sound source is located using adirectional microphone. Since most noises at a factory or the like aresounds having a low frequency range as described above, they have lowdirectionability and even when a microphone is provided withdirectionability, it is difficult to locate a sound source.

[0008] In view of the above problems of the prior art, it is an objectof the present invention to provide a sound source locating system whichis simple in structure and can locate and display the source of a soundsuch as a noise at a factory or the like with high accuracy even when itis outside.

SUMMARY OF THE INVENTION

[0009] According to a first aspect of the present invention, there isprovided a sound source locating system which comprises microphonesincluding three microphones arranged two-dimensionally, means ofestimating the location of a sound source from phase differences amongthe output signals of the microphones (such as information on the phaseangle of the cross spectrum of the output signals), means of picking upan image around the estimated location of the sound source and means ofdisplaying the above estimated location of the sound source on thepicked up image in order to estimate the location of the sound sourceand display the estimated location of the sound source on the imagearound the location of the sound source displayed on the display meanssuch as a display.

[0010] According to a second aspect of the present invention, there isprovided a sound source locating system, wherein a pair of microphonesspaced apart from each other by a predetermined distance are eachdisposed on two crossing straight lines, for example, a pair ofmicrophones are placed at X1=(L₁/2, 0) and X2=(−L₁/2, 0) on the X axisand the other pair of microphones are placed at Y1=(0, L₂/2) and Y2=(0,−L₂/2) on the Y axis, a difference between sound arrival times to eachpair of microphones is obtained, and the direction of the sound sourceis estimated from the above arrival time differences.

[0011] According to a third aspect of the present invention, there isprovided a sound source locating system which comprises microphonesincluding four microphones arranged three-dimensionally, means ofestimating the location of a sound source from phase differences amongthe output signals of the microphones, means of picking up an imagearound the estimated location of the sound source and means ofdisplaying the estimated location of the sound source on the picked upimage.

[0012] According to a fourth aspect of the present invention, there isprovided a sound source locating system, wherein a pair of microphonesspaced apart from each other by a predetermined distance are eachdisposed on three crossing straight lines, a difference between soundarrival times to each pair of microphones is obtained, and the locationof the sound source is estimated from the above arrival timedifferences.

[0013] According to a fifth aspect of the present invention, there isprovided a sound source locating system which comprises microphonesconsisting of two pairs of microphones disposed on two crossing straightlines with a predetermined distance therebetween and a fifth microphonenot existent on the same plane as the above two pairs of microphones,means of estimating the location of a sound source from phasedifferences among the output signals of the microphones, means ofpicking up an image around the estimated location of the sound sourceand means of displaying the estimated location of the sound source onthe picked up image in order to estimate the location of the soundsource from differences among sound arrival times to the microphonesobtained from the above phase differences and display the estimatedlocation of the sound source on the image around the location of thesound source displayed on the display means such as a display.

[0014] According to a sixth aspect of the present invention, there isprovided a sound source locating system, wherein the above two pairs ofmicrophones are disposed on two crossing straight lines, respectively,to form a regular square, the fifth microphone is disposed on a straightline passing through the center of the regular square and perpendicularto the above two straight lines to make the distances between the fifthmicrophone and the microphones forming the square equal to one another,and differences among sound arrival times to the microphones areobtained to estimate the location of the sound source.

[0015] According to a seventh aspect of the present invention, there isprovided a sound source locating system, wherein the fifth microphone isarranged such that the distances between the fifth microphone and theother microphones forming the regular square are made equal to thedistance between each pair of the microphones.

[0016] According to an eighth aspect of the present invention, there isprovided a sound source locating system, wherein the color of a symbolfor the location of the sound source displayed is changed according tothe level of sound pressure or the height of frequency. This makes itpossible to display not only the locations of a plurality of soundsources when existent but also the sound pressure levels and frequencycharacteristics of the sound sources. Therefore, it is possible to judgethe characteristic features of the sound sources visually.

[0017] According to a ninth aspect of the present invention, there isprovided a sound source locating system, wherein the microphones aremoved to a plurality of positions, thereby improving the estimationaccuracy of the location of the sound source.

[0018] According to a tenth aspect of the present invention, there isprovided a sound source locating system, wherein the microphones arerotated to collect sounds at a plurality of angles, thereby improvingthe estimation accuracy of the location of the sound source.

[0019] According to an eleventh aspect of the present invention, thereis provided a sound source locating system, wherein the microphones areused to collect a sound at predetermined time intervals to obtain thelocation of the sound source at each measurement time in order toestimate the movement of the location of the sound source.

[0020] According to a twelfth aspect of the present invention, there isprovided a sound source locating system which comprises means ofmeasuring the absolute locations on the ground of the microphones tospecify the absolute location on the ground of the sound source from themeasurement locations of the microphones.

[0021] According to a thirteenth aspect of the present invention, thereis provided a sound source locating system which comprises means ofstoring data on the sound pressure of a sound source which is collectedby the microphones and normal and means of comparing newly collectedsound pressure data with the above stored sound pressure data.

[0022] Other objects and advantages of the present invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0023]FIG. 1 is a schematic diagram of a sound source locating systemaccording to Embodiment 1 of the present invention;

[0024]FIG. 2 is a functional block diagram of the storing/computing unitof a personal computer according to Embodiment 1 of the presentinvention;

[0025]FIG. 3 is a diagram showing the arrangement of microphonesaccording to Embodiment 1 of the present invention;

[0026]FIG. 4 is a diagram for explaining the movement of a measurementunit:

[0027]FIG. 5 is a flow chart of a sound source locating method accordingto Embodiment 1 of the presents invention;

[0028]FIG. 6 is a diagram showing an example of a display imageaccording to Embodiment 1 of the present invention;

[0029]FIG. 7 is a schematic diagram of a sound source locating systemaccording to Embodiment 2 of the present invention;

[0030]FIG. 8 is a diagram showing the arrangement of microphonesaccording to Embodiment 2 of the present invention; and

[0031]FIG. 9 is a diagram showing an example of a display imageaccording to Embodiment 2 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings.

EMBODIMENT 1

[0033]FIG. 1 is a schematic diagram of a sound source locating systemaccording to Embodiment 1. M1 to M4 are microphones for measuring thesound pressure level of a noise from an unshown sound source, M0 is anauxiliary measuring microphone, 11 a CCD camera for picking up an imagearound the location of the sound source (to be simply referred to as“camera” hereinafter), 12 GPS for specifying the ground positions of theabove microphones M0 to M4, 13 amplifier for amplifying sound pressuresignals collected by the above microphones M0 to M4, 14 A/D converterfor converting the amplified sound pressure signals (analog signals)into digital signals, and 15 a video input/output unit for convertingthe image signal (analog signal) of the camera 11 into a digital signal.

[0034] Denoted by 20 is a personal computer which comprises a keyboard21 as input means, a storing/computing unit 22 for computing theestimation of the location of the sound source and a display 23 as imagedisplay means. The above storing/computing unit 22 comprises parameterstorage means 24 for storing measurement parameters, sound sourcelocation estimating means 25 for estimating the location of the soundsource by a hyperbolic technique using the A/D converted sound pressuresignals of the microphones M1 to M4 and image composing means 26 forcomposing an image by adding an image showing the estimated location ofthe sound source to an image from the above camera 11 and sending it tothe above display 23.

[0035]30 denotes a base which comprises a support member 31 composed ofa tripod and a rotary frame 32, disposed on the top of the supportmember 31, for mounting the microphones M0 to M4, the microphone M0 ismounted to the top of a vertical frame 32Z projecting upward from therotary plate 32P of the above rotary frame 32, and the microphones M1 toM4 are mounted to both ends of two horizontal frames 32X and 32Ycrossing each other and projecting from the above vertical frame 32Z.The camera 11 is mounted to a lower portion of the above vertical frame32Z and rotated together with the above microphones M0 to M4. GPS 12 ismounted on a mounting plate 33 attached below the above rotary frame 32.

[0036] The base 30 mounting the above microphones M0 to M4, the camera11 and GPS12 is called “measurement unit 10” hereinafter.

[0037] The hyperbolic technique is used to estimate the location of theabove sound source, making use of the fact that the location (x, y, z)of the sound source is on the surface of a spindle whose axis is astraight line passing through a pair of microphones (Mi, Mj) and whichis determined by a constant calculated from a difference between soundarrival times to the pair of microphones at a predetermined distancefrom the sound source (time delay Dij), a distance between themicrophones and sound velocity. A pair of microphones spaced apart fromeach other by a predetermined distance are each disposed on threecrossing straight lines to obtain a difference between sound arrivaltimes to each pair of microphones, and at least three spindles areobtained from the above arrival time differences to obtain the location(x, y, z) of the sound source from the intersecting point of thesespindles.

[0038] In this Embodiment 1, the direction of the sound source isestimated based on the assumption that the sound source is situated onthe X-Y plane. Therefore, as shown in FIGS. 3(a) and 3(b), a pair ofmicrophones (M1, M3) and another pair of microphones (M2, M4) are placedat points (L/2, 0, 0) and (−L/2, 0,0) on the X axis and at points (0,L/2, 0) and (0, −L/2, 0) on the Y axis with a distance L therebetween,respectively, and the frequencies of output signals from the pairs ofmicrophones (M1, M3) and (M2, M4) are analyzed to estimate the locationof the sound source from a time delay Dij (differences Dx and Dy betweensound arrival times to the pair of microphones (M1, M3) and betweensound arrival times to the pair of microphones (M2, M4) in thisembodiment) between the microphone Mi and the microphone Mj at afrequency f.

[0039] When the distance from the above sound source to the system ismuch larger (for example, 10 times or more) than the distance L betweenthe microphones, it is possible that the sound is regarded as a planewave and the direction θ of the sound source is represented by thefollowing approximation (1).

θ=tan⁻¹(Dy/Dx)   (1)

[0040] The above time delay Dij is calculated from the followingequation (2) by obtaining the cross spectrum Pij (f) of a signal inputinto the two microphones Mi and Mj and using the phase angle informationψ(rad) of the above frequency f.

Dij=1/(2πf)ψ[Pij(f)](sec)   (2)

[0041] The direction θ of the sound source can be calculated for eachfrequency.

[0042] The distance L between the pair of microphones (M1, M3) andbetween the pair of microphones (M2, M4) is determined according to themain frequency range of the noise to be measured. In this Embodiment 1,the above noise to be analyzed is a sound having a peak at 120 Hz, 240Hz and 360 Hz generated from a transformer at a factory or the like (apeak at 60 Hz which is a fundamental wave is excluded because itsbackground is large) and the above L is set to 0.42 m so that a noisehaving a frequency band of about 490 Hz or less can be measured withhigh sensitivity.

[0043] The auxiliary measuring microphone M0 having a height differentfrom those of the microphones M1 to M4 is used to measure an impulsesignal as a TPS signal (time delaying pulse signal) in order to confirmthe influence of a reflection wave.

[0044] Although the above direction θ of the sound source can beobtained by one time of measurement, in this Embodiment 1, as shown inFIG. 4, the measurement accuracy of the direction θ of the sound sourceis improved by moving the measurement unit 10 to a plurality ofpositions, or by rotating the rotary frame 32 at the same measurementposition to carry out measurement at a plurality of angles.

[0045] A description is subsequently given of the method of estimatingthe direction of a sound source using the above sound source locatingsystem with reference to the flow chart of FIG. 5.

[0046] After the measurement unit 10 is first installed at a positionwhere a noise from its source can be collected, the adjustment of thesystem such as the frequency range of an input signal and the lens ofthe camera is carried out (step S10). At this point, the horizontalframe 32X (or horizontal frame 32Y) is adjusted to a predetermined startposition (provisional, X axis or Y axis).

[0047] Thereafter, parameters such as the number of microphones and thesampling frequency are stored in the parameter storage means 24 in thestoring/computing unit 22 of the personal computer 20 from the keyboard21 (step S11). The above parameters also include information on thearrangement of the microphones, the frequency range passing through anunshown filter and the maximum average number of measurement timesbesides the number of measurement positions, the number of microphonesand the sampling frequency. Since the parameter storage means 24 storesthese initial set values, only changed parameters are input into thisparameter storage means 24.

[0048] Subsequently, the center positions of the microphones M0 to M4,that is, the absolute positions on the ground of the microphones aremeasured by GPS 12 mounted to the measurement unit 10 and input into thepersonal computer 20 (step S12), and then the number of measurementtimes and the rotation angle of the frame at the above measurementposition are input from the keyboard 21 (step S13). The level of soundpressure (sound information) and image information may be collected byrotating the rotary frame 32 each time measurement is made or byrotating the rotary frame 32 after measurement is made a plurality oftimes at the same angle.

[0049] In this Embodiment 1, sound information and image information arecollected once at a frame rotation angle of 0 ° (initial position), 90°,180° or 270° by means of the microphones M1 to M4 and the camera 11, andthe collected sound information and image information are input into thepersonal computer 20 (step S14). That is, in this embodiment, themeasurement conditions are set such that measurement is carried out fourtimes at that position. Sound pressure signals which are the outputs ofthe microphones M1 to M4 and the microphone M0 are amplified by theamplifier 13 and converted into digital signals by the A/D converter 14.An image signal from the camera 11 is converted into a digital signal bythe video input/output unit 15 and then input into the personal computer20.

[0050] The personal computer 20 carries out computation for theestimation of the location of the sound source using sound informationfrom the above microphones M1 to M4, the above-described hyperbolictechnique or the approximation (1) for the direction θ of the soundsource (step S15).

[0051] Subsequently, it is judged whether measurement at all the framerotation angles is completed (step S16) and when it is not, the rotaryframe 32 is rotated at 90° and the routine returns to step S14 tocollect sound information and image information at the next framerotation angle. When measurement at all the frame rotation angles iscompleted, the rotary frame 32 is returned to the initial position andthe processing of averaging the locations of the sound source obtainedat all the measurement positions is carried out (step S17).

[0052] Thereafter, it is judged whether measurement at all themeasurement points is completed (step S18) and when it is not, themeasurement unit 10 is moved to the next measurement position to carryout the operations of the above steps S12 to S17.

[0053] When measurement at all the measurement points is completed, themost reliable location of the sound source is estimated from data on thelocation of the sound source at each measurement point (step S19) andthen an image which shows the estimated location of the sound source thebest is selected to display the sound source location estimation area onthe image as shown in FIG. 6 (step S20).

[0054] Even when there are a plurality of sound sources, the soundsource locating system of the present invention can specify thelocations of the plurality of sound sources and calculate thecontribution rates of the sound sources to each frequency. For example,it can compute and display the locations of the plurality of soundsources such as the estimated area A of the location of a sound sourcewhich is located at “0°” in the forward direction and the estimated areaB of the location of a sound source which is located at “−45°” in therear direction and detailed information on the sound sources such as theintensity of each sound having a different frequency at an angle fromthe measurement position. It is possible to change the color of a symbolfor the location of a sound source displayed according to the level ofsound pressure or the height of frequency. For example, to change thecolor of a symbol for the location of a sound source displayed accordingto the level of sound pressure, the symbol (circle) colored according tothe level of sound pressure is displayed on the image that shows thelocation of the sound source the best, a frequency distribution graphwhich plots the direction of the sound source on the X axis andfrequency on the Y axis b is displayed below the image, and symbols inthe graph are colored different corresponding to each level of soundpressure so that even when there are a plurality of sound sources whichdiffer from one another in sound pressure level or frequency, thelocations of the sound sources can be known visually, thereby making itpossible to know the characteristic features of the sound sources indetail easily.

[0055] A symbol colored according to the height of frequency may bedisplayed on the image that shows the location of the sound source thebest and a sound pressure distribution graph which plots the directionof the sound source on the X axis and the level of sound pressure on theY axis may be displayed below this image. Symbols in the above graph maybe colored different according to the height of frequency

[0056] The coordinates of the estimated location of the sound source maybe displayed at the same time. The above coordinates may be values fromthe preset origin (0,0) or the absolute position on the ground of theestimated location of the sound source calculated based on the locationof the measurement unit 10 measured by the above GPS 12.

[0057] Thus, according to this Embodiment 1, the direction of the soundsource is estimated from a difference between the output signal arrivaltimes of the pair of microphones (M1, M3) disposed on the X axis with adistance L therebetween and a difference between the output signalarrival times of the pair of microphones (M2, M4) disposed on the Y axiswith the distance L therebetween, and an image around the estimatedlocation of the sound source is picked up by the camera 11 so that theestimated location of the sound source is displayed on the picked upimage displayed on the display 23 of the personal computer 20.Therefore, the source of a sound such as a noise at a factory or thelike can be specified and displayed accurately with a simple structureeven when it is outside. By changing the color of a symbol for thelocation of a sound source displayed as an image according to the levelof sound pressure or the height of frequency, even when there are aplurality of sound sources, the locations of the sound sources can bespecified and the characteristic features of the sound sources can beknown visually.

[0058] The measurement accuracy of the direction θ of the sound sourcecan be improved by moving the measurement unit 10 comprising themicrophones M0 to M4, the camera 11 and GPS 12 mounted on the base 30 toa plurality of positions, or by rotating the rotary frame 32 to measureat a plurality of angles and at the same measurement position.

[0059] In the above Embodiment 1, four microphones are used to estimatethe direction of the sound source. However, three microphones which arenot disposed on a straight line (on a plane) may be used to estimate thedirection of the sound source.

[0060] In the above embodiment, two pairs of microphones (M1, M3) and(M2, M4) are used to estimate the direction of the sound source.Further, three pairs of microphones including another pair ofmicrophones disposed in the Z-axis direction may be used to obtain thehorizontal angle θ and elevation angle φ of the location of the soundsource. Theoretically, the location of a sound source can be estimatedby using four microphones arranged three-dimensionally on three crossingstraight lines. However, to facilitate signal processing andcomputation, three pairs of microphones which are spaced apart from eachother by a predetermined distance are preferably disposed on threestraight lines, namely, X axis, Y axis and Z axis to estimate thelocation of the sound source.

[0061] In the above embodiment, the rotary frame 32 is rotated at eachmeasurement position for measurement. Even when the measurement unit 10is moved to a plurality of positions without rotating the rotary frame32 or when the rotary frame 32 is rotated at the same measurementposition without moving the measurement unit 10 to a plurality ofpositions, the direction θ of the sound source can be measuredaccurately. When the rotary frame 32 is not rotated, the optimum imagearound the sound source must be picked up by turning the camera 11toward the estimated direction of the sound source.

[0062] It is needless to say that the distance L between the microphonesis not limited to 0.42 m and may be suitably determined according to theproperties of the sound source.

[0063] The movement of the sound source can be estimated by collecting asound at predetermined time intervals at one measurement position ormeasurement angle to obtain the location of the sound source at eachmeasurement time.

EMBODIMENT 2

[0064]FIG. 7 is a schematic diagram of a sound source locating systemaccording to Embodiment 2. In this Embodiment, five microphones M1 to M5arranged in a square columnar form are used to estimate the horizontalangle θ and elevation angle φ of the sound source. Although otherelements are the same as in the above Embodiment 1, in this Embodiment2, sound information from the above microphones M1 to M5 is used toestimate the location of the sound source by means of the personalcomputer 20.

[0065] A description is subsequently given of an example of thearrangement of the microphones M1 to M5.

[0066] As shown in FIG. 7 and FIG. 8, the microphones M1 to M4 aredisposed above the above rotary frame 32 (in the Z-axis direction) sothat their detection portions form a regular square with the origin O onthe X-Y plane as the center thereof. Specifically, the detectionportions of the microphones M1 and M3 are placed at points (L/2, 0, 0)and (−L/2, 0, 0) on the X axis and the detection portions of themicrophones M2 and M4 are placed at points (0, L/2, 0) and (0, −L/2, 0)on the Y axis perpendicular to the X axis.

[0067] As shown in FIG. 7 and FIG. 8, the fifth microphone M5 is held tothe end of a substantially L-shaped member 32T projecting from the sideof the above rotary frame 32 and extending upward and its detectionportion is located above the center of the regular square constituted bythe above four microphones M1 to M4. The coordinates of the detectionportion of the microphone M5 are shown below.

[0068] (0, 0, L)

[0069] Thereby, the microphones M1 to M5 are disposed such that thedistances between the fifth microphone and the microphones M1 to M4should be equal to the distance L between the microphones (M1, M3) andthe distance L between the microphones (M2, M4). In this embodiment, theabove L is set to 0.35 m so that a noise from a transformer at a factoryor the like can be measured with high sensitivity.

[0070] A description is subsequently given of the method of estimatingthe location of a sound source.

[0071] In the actual measurement, as the location of the sound source isvery far from the locations of the microphones, a sound that reaches themicrophones can be regarded as a plane wave. Then, in this embodiment,to obtain the location of the sound source, the location of the soundsource is estimated based on the assumption that the location of thesound source is very far (for example, 10 times or more the distance L)from the locations of the microphones and the sound is input into themicrophones as a plane wave.

[0072] In the approximation of the plane wave, since a time delay Dijbetween the microphone Mi and the microphone Mj and the horizontal angleθ and elevation angle φ of the location of the sound source arerepresented by the following equations (3) and (4), the frequencies ofthe output signals of the microphones M1 to M5 are analyzed to calculatedifferences (time delay) Dij in sound arrival time among the microphonesM1 to M5 at a frequency f to obtain the above horizontal angle θ andelevation angle φ.

θ=tan⁻¹(D 13/D 24)   (3)

φ=tan⁻¹   (4)

[0073] The above time delay Dij is the same as in the above embodiment 1and calculated using the above equation (2).

[0074] The location of the sound source can be calculated for eachfrequency.

[0075] Thereby, an image around the above estimated location of thesound source is picked up by the camera 11 so that the estimatedlocation of the sound source can be displayed on the display 23 of thepersonal computer 20.

[0076] The method of estimating the location of a sound source is almostthe same as in the above embodiment 1 except that the personal computer20 uses sound information from the above microphones M1 to M5 toestimate the horizontal angle θ and elevation angle φ of the location ofthe sound source by the above-described method of estimating thelocation of a sound source.

[0077]FIG. 9 shows an example of an image showing the location of asound source according to Embodiment 2. In this Embodiment, thehorizontal angle θ is plotted on the X axis and the elevation angle φ isplotted on the Y axis of the image around the sound source displayed anda symbol for the location of the sound source on the above coordinates(θ, φ) can be displayed.

[0078] The color of the symbol for the location of the sound sourcedisplayed can be changed according to the level of sound pressure or theheight of frequency. For example, when the symbol for the location ofthe sound source displayed is changed according to the level of soundpressure, symbols (circles) colored different according to the level ofsound pressure are displayed on an image that shows the location of thesound source the best, a frequency distribution graph which plots thedirection of the sound source on the X axis and frequency on the Y axisis displayed below the image, and symbols in the graph are coloreddifferent according to the level of sound pressure so that even whenthere are a plurality of sound sources which differ from one another inthe level of sound pressure or frequency, the locations of these soundsources can be known visually, thereby making it possible to know thecharacteristic features of the sound sources in detail easily.

[0079] Also, symbols colored different according to the height offrequency may be displayed on the image that shows the location of asound source the best and a sound pressure distribution graph whichplots the direction of the sound source on the X axis and the level ofsound pressure on the Y axis may be displayed below the image. Symbolsin the graph may be colored different according to the height offrequency.

[0080] In the above Embodiment 2, the microphones M1 to M5 are disposedsuch that the distances between the fifth microphone M5 and the othermicrophones M1 to M4 should be equal to the distance L between themicrophones (M1, M3) and the distance L between the microphones (M2,M4). The method of arranging the microphones is not limited to this.Basically, the above distances may not be equal to one another, twopairs of microphones are disposed on two crossing straight lines, andfurther the fifth microphone may be placed at a position not on the sameplane as the above pairs of microphones. To facilitate computation forthe estimation of the direction of the sound source, it is preferredthat the microphones should be located at highly symmetrical positions.It is particularly preferred that the above two pairs of microphonesshould be disposed on two crossing straight lines so that they form aregular square, the fifth microphone should be disposed on a straightline passing through the center of the above regular square andperpendicular to the above straight lines, and the distances between thefifth microphone and the microphones forming the above regular squareshould become equal to one another.

[0081] In the sound source locating system of Embodiments 1 and 2, sincethe contribution rates of a plurality of sound sources to each frequencycan be calculated as described above, when the system of the presentinvention comprises means of storing data on the sound pressure of asound source which is normal and collected by the above microphones andmeans of comparing the above stored sound pressure data with newlycollected sound pressure data, it can specify the location of a soundsource which generates an abnormal sound, for example, the soundpressure level of a specific frequency of the newly collected soundpressure level data becomes higher than the past data or a new peakappears at a frequency band where no peak has ever been seen. Therefore,a sound source abnormality detection system is constructed by using thissound source locating system of the present invention and installed at apredetermined site within the premises of a factory to measure thelocation of a sound source regularly so that a sound source whichgenerates an abnormal sound by a failure in a transformer or motor canbe located, thereby making it possible to detect the abnormality of anoise generating device.

INDUSTRIAL FEASIBILITY

[0082] As described above, according to the present invention, thelocation of a sound source is estimated from phase differences among theoutput signals of microphones including three microphones arrangedtwo-dimensionally or four microphones arranged three-dimensionally, andan image around the above estimated location of the sound source ispicked up so that the estimated location of the sound source isdisplayed on the picked up image. Therefore, the sound source can belocated and displayed with a simple structure.

[0083] A pair of microphones arranged with a predetermined spacetherebetween are each disposed on two or three crossing straight linesand a difference between sound arrival times to each pair of microphonesis obtained to estimate the direction or location of the sound sourceusing the hyperbolic technique or the approximation (plane waveapproximation) of the direction of the sound source from the abovearrival time differences in order to specify the direction or thelocation of the sound source accurately.

[0084] The location of the sound source is estimated from phasedifferences among the output signals of microphones consisting of twopairs of microphones disposed on two crossing straight lines with apredetermined space therebetween and a fifth microphone not existent onthe same plane as the two pairs of microphones and an image around theestimated location of the sound source is picked up so that theestimated location of the sound source is displayed on the above image.Therefore, the sound source can be located and displayed with a simplestructure.

[0085] The above two pairs of microphones are disposed on two crossingstraight lines to form a regular square, the fifth microphone is locatedon a straight line passing through the center of the regular square andperpendicular to the above two straight lines, the distances between thefifth microphone and the microphones forming the regular square becomeequal to one another, and differences between sound arrival times to oneof the pairs of microphones and between sound arrival times to the otherpair of microphones are obtained to estimate the location of the soundsource. Therefore, the direction or location of the sound source can bespecified accurately.

[0086] When the fifth microphone is located such that the distancesbetween the fifth microphone and the other microphones forming the aboveregular square become equal to the distance between the microphones ofeach pair, the distances between the pairs of the microphones forobtaining differences in arrival time can be made equal to each other,thereby making much easier computation for the estimation of thelocation of the sound source.

[0087] By changing the color of a symbol for the location of the soundsource displayed on the image according to the level of sound pressureor the height of frequency, even when there are a plurality of soundsources, not only the locations of these sound sources but also thesound pressure levels and frequency characteristics of the sounds can bedisplayed. Therefore, the characteristic features of the sound sourcescan be judged visually.

[0088] Since the location of a sound source which generates an abnormalsound is specified by providing means of storing data on the soundpressure of a sound source which is normal and collected by the abovemicrophones and means of comparing newly collected sound pressure datawith the above stored sound pressure data, the abnormality of a noisegenerating device can be detected without fail.

[0089] Further, since the microphones are moved to a plurality ofpositions or the microphones are rotated to measure at a plurality ofpoints or at a plurality of angles, the estimation accuracy of thelocation of the sound source can be improved.

[0090] Since a sound is collected at predetermined time intervals toobtain the location of the sound source at each measurement time, themovement of the location of the sound source can be estimated.

[0091] Since locating means such as GPS for measuring the absolutepositions on the ground of the microphones is provided, the absoluteposition on the ground of the location of the sound source can bespecified.

What is claimed is:
 1. A sound source locating system which comprisesmicrophones including three microphones arranged two-dimensionally,means of estimating the location of a sound source from phasedifferences among the output signals of the microphones, means ofpicking up an image around the estimated location of the sound sourceand means of displaying the estimated location of the sound source onthe picked up image.
 2. The sound source locating system of claim 1,wherein a pair of microphones spaced apart from each other by apredetermined distance are each disposed on two crossing straight lines,a difference between sound arrival times to each pair of microphones isobtained, and the direction of the sound source is estimated from thearrival time differences.
 3. A sound source locating system whichcomprises microphones including four microphones arrangedthree-dimensionally, means of estimating the location of a sound sourcefrom phase differences among the output signals of the microphones,means of picking up an image around the estimated location of the soundsource and means of displaying the estimated location of the soundsource on the picked up image.
 4. The sound source locating system ofclaim 3, wherein a pair of microphones spaced apart from each other by apredetermined distance are each disposed on three crossing straightlines, a difference between sound arrival times to each pair ofmicrophones is obtained, and the location of the sound source isestimated from the arrival time differences.
 5. The sound sourcelocating system of claim 3 which comprises microphones consisting of twopairs of microphones disposed on two crossing straight lines with apredetermined distance therebetween and a fifth microphone not existenton the same plane as the two pairs of microphones, means of estimatingthe location of a sound source from phase differences among the outputsignals of the microphones, means of picking up an image around theestimated location of the sound source and means of displaying theestimated location of the sound source on the picked up image.
 6. Thesound source locating system of claim 5, wherein the two pairs ofmicrophones are disposed on two crossing straight lines, respectively,to form a regular square, the fifth microphone is disposed on a straightline passing through the center of the regular square and perpendicularto the two straight lines, and differences among sound arrival times tothe microphones are obtained to estimate the location of the soundsource.
 7. The sound source locating system of claim 6, wherein thefifth microphone is arranged such that the distances between the fifthmicrophone and the other microphones forming the regular square are madeequal to the distance between each pair of the microphones.
 8. The soundsource locating system of any one of claims 1 to 7, wherein the color ofa symbol for the location of the sound source displayed is changedaccording to the level of sound pressure or the height of frequency. 9.The sound source locating system of any one of claims 1 to 8, whereinthe microphones are moved to a plurality of positions.
 10. The soundsource locating system of any one of claims 1 to 8, wherein themicrophones can be rotated.
 11. The sound source locating system of anyone of claims 1 to 10, wherein the microphones are used to collect asound at predetermined time intervals to estimate the movement of thelocation of the sound source.
 12. The sound source locating system ofany one of claims 1 to 11 which comprises means of measuring theabsolute locations on the ground of the microphones.
 13. The soundsource locating system of any one of claims 1 to 7 which comprises meansof storing data on the sound pressure of a sound source which iscollected by the microphones and normal and means of comparing newlycollected sound pressure data with the stored sound pressure data.